1. Field of the Invention
The present invention relates to a sheathed endoscope which is designed so that an insert part of the endoscope is covered with a sheath that can be replaced with a new one each time the endoscope has been used in order to prevent the transmission of bacteria and viruses from one patient to another through the endoscope. The present invention also relates to a sheath that is used for the above-described sheathed endoscope.
The present disclosure relates to subject matter contained in Japanese patent application Nos. 1-335534 and 1-335535 (both filed on Dec. 25, 1989) which are expressly incorporated herein by reference in their entirety.
2. Description of the Prior Art
A common sheath that is used for a sheathed endoscope comprises a tube and a transparent distal end cover that is attached to the distal end of the tube, and that is removably fitted over an elongate insert part of the endoscope.
However, when such a sheath is merely fitted over the insert part of an endoscope, a gap may be produced between the distal end cover and the distal end face of the insert part during use. In particular, a sheathed endoscope in which an end portion of a forceps inserting channel for inserting a tool for an endoscopic procedure, for example, a biopsy forceps, is connected to the distal end cover of the sheath involves the problem that the distal end cover may be strongly pushed forward by the forceps inserting channel during use, resulting in a large gap between the distal end cover and the distal end face of the insert part.
Such a sheathed endoscope has a viewing window and illuminating windows, which are provided at the distal end of the insert part, and both an observation light and an illuminating light pass through the transparent distal end cover. Accordingly, if a gap is produced between the distal end cover 251 of the sheath and the distal end face 261 of the insert part of the endoscope, as shown in FIG. 9, part of the illuminating light that is emitted from the illuminating windows 262 enters the viewing window 263 after being reflected at the inner surface of the distal end cover 251. In such a case, an intense flare or ghost may appear in the observation field of view, thus degrading the observation capabilities of the endoscope.
In order to prevent this problem, the distal end cover must be secured to the distal end of the insert part. However, the insert part of the endoscope must be formed as thin as possible with a view to minimizing the pain given to the patient. It is therefore almost impossible to secure the distal end cover to the distal end of the insert part by means, for example, of screws, because of the limited space. In addition, it would be troublesome to untighten and tighten screws for each endoscopic procedure.